let _Vue = null

const genHashRoute = to => to.replace(/^\/(.*?)/, '/#$1')

export default class VueRouter {
  static install (Vue) {
    // 1. 判断当前插件是否已安装
    if (VueRouter.install.installed) {
      return
    }

    VueRouter.install.installed = true

    // 2. 把 Vue 构造函数记录到全局变量
    _Vue = Vue

    // 3. 把创建 Vue 实例的时候传入的router对象注入到 Vue 实例上
    // 混入
    _Vue.mixin({
      beforeCreate () {
        if (this.$options.router) {
          _Vue.prototype.$router = this.$options.router
          this.$options.router.init()
        }
      }
    })
  }

  constructor (options) {
    this.options = options
    this.routeMap = {}
    this.data = _Vue.observable({
      current: '/#'
    })
  }

  init () {
    this.createRouteMap()
    this.initComponents(_Vue)
    this.initEvent()
  }

  createRouteMap () {
    const { routes } = this.options

    // 遍历所有的路由规则，把路由规则解析成键值对的形式 存储到 routeMap 中
    this.routeMap = Object.fromEntries(routes.map(({ path, component }) => [genHashRoute(path), component]))
  }

  initComponents (Vue) {
    Vue.component('router-link', {
      props: {
        to: String
      },
      render (h) {
        return h('a', {
          attrs: {
            href: genHashRoute(this.to)
          },
          on: {
            click: this.clickHandler
          }
        }, [this.$slots.default])
      },
      methods: {
        clickHandler (e) {
          const hashRoute = genHashRoute(this.to)

          history.pushState({}, '', hashRoute)
          this.$router.data.current = hashRoute

          e.preventDefault()
        }
      }
    })

    const self = this

    Vue.component('router-view', {
      render (h) {
        const component = self.routeMap[self.data.current]

        return h(component)
      }
    })
  }

  initEvent () {
    window.addEventListener('popstate', () => {
      this.data.current = window.location.pathname
    })
  }
}
